1. Field of the Invention
The present invention generally relates to golf balls and more particularly to golf balls having cores made of polyalkenamer and polybutadiene rubber blends. Single-layer and multi-layered cores may be made. The golf ball includes a cover that may be single or multi-layered. More particularly, the polyalkenamer rubber has a Mooney viscosity of less than about 10 and the polybutadiene rubber has a Mooney viscosity of about 50 to about 150.
2. Brief Review of the Related Art
Manufacturers of golf balls are constantly looking at new materials for developing multi-piece, solid balls. Basically, a two-piece solid golf ball includes a solid inner core protected by an outer cover. The inner core is made commonly of a rubber material such as natural and synthetic rubbers, styrene butadiene, polybutadiene, poly(cis-isoprene), poly(trans-isoprene), or highly neutralized acid copolymers. The outer cover is made commonly of ionomer resins, polyamides, polyesters, polyurethanes, or polyureas. In other instances, a four-piece solid golf ball having an inner core and surrounding outer core layer (dual-core) is made. The ball further includes an intermediate layer and outer cover. Five-piece balls having a dual-core, surrounding intermediate layer, and multi-layer cover comprising an inner cover and outer cover also are known in the industry. Different materials can be used to impart specific properties and features to the balls.
For example, the resiliency and rebounding performance of the golf ball is based primarily on the core of the ball. The core acts as an “engine” for the ball. In general, the rebounding performance of the ball is based on its initial velocity after being struck by the face of the golf club and its outgoing velocity after making impact with a hard surface. More particularly, the “coefficient of restitution” or “COR” of a golf ball refers to the ratio of a ball's rebound velocity to its initial incoming velocity when the ball is fired out of an air cannon into a rigid vertical plate. The COR for a golf ball is written as a decimal value between zero and one. A golf ball may have different COR values at different initial velocities. The United States Golf Association (USGA) sets limits on the initial velocity of the ball so one objective of golf ball manufacturers is to maximize COR under these conditions. Balls with a higher rebound velocity have a higher COR value. Such golf balls rebound faster, retain more total energy when struck with a club, and have longer flight distance.
Golf ball manufacturers have looked at using blends of polybutadiene rubbers to make cores. For example, Voorheis et al., U.S. Pat. Nos. 6,982,301 and 6,774,187 disclose a golf ball containing a core formed from a polybutadiene blend comprising: a) a first polybutadiene formed with a cobalt or nickel catalyst having a first Mooney viscosity between about 50 and about 150; and b) a second polybutadiene formed with a lanthanide series catalyst having a second Mooney viscosity between about 30 and about 100.
In addition, Kim et al., U.S. Pat. No. 7,528,196 and U.S. Patent Application Publication US 2009/0191981 disclose a golf ball comprising a core, cover layer, and optionally one or more inner cover layers, wherein at least one portion of the ball comprises a blend of a polyalkenamer and polyamide. The polyalkenamer/polyamide composition contains about 2 to about 90 weight % of polyalkenamer polymer and about 10 to about 98 weight % of polyamide. The '196 patent and '981 Published Application further disclose that the polyalkenamer/polyamide composition may be blended with other rubber polymers including polybutadiene, polyisoprene, polychloroprene, polybutylene, and styrene-butadiene rubber prior to molding. However, neither the '196 patent nor '981 Published Application discloses a composition comprising about 51 to about 99 weight percent of a low Mooney viscosity polyalkenamer rubber, and about 1 to about 49 weight percent of a high Mooney viscosity polybutadiene rubber.
One objective of the present invention is to develop compositions that can be used to make a core for a golf ball, wherein the core provides the ball with high resiliency along with a comfortable and soft “feel.” The present invention provides golf ball core compositions having such properties as well as other advantageous characteristics, features, and benefits.